1. Field of the Invention
This invention relates to a method for excavating drifts, tunnels, stopes, caverns and the like with tools such as disc cutters, operating in an undercutting manner on a rock face, and a machine for performing such excavation.
2. Description of the Prior Art
Undercutting disc cutters working from a pilot bore-hole or opening are known as an effective cutting system, since in such a case, it is not the high compressive strength of the rock which must be overcome, but rather only its low tensile strength. A tunnelling machine with a rotary head is known (DE 31 40 707 A1), which has a pilot borer located on the front of the head working in a conventional manner (i.e. using a conventional drilling head) and spaced behind it in the axial direction, a plurality of tool supports are provided which are formed as radially pivotable arms. Disc cutters mounted on these arms start from a centrally located pilot hole in order to cut the rock in an undercutting manner with a radial pivoting-out motion of the arms. To cut the pilot hole with a relatively large diameter using a conventional drilling head requires a great deal of effort and is difficult to achieve concurrently with the operation of the disc cutters working in the undercutting mode. It is also considered disadvantageous that the pilot bore-hole drilling process requires high thrust.
In another known tunnelling machine (DE 87 17 189 U1), two pivotable supporting arms equipped with disc cutters are mounted parallel to one another on a rotary head in such a manner that they are located on either side of a diameter line of the head. The pivot points of the supporting arms are located on the periphery of the head, in such a manner that the supporting arms face one another. Instead of drilling a pilot hole, in this case each of the two disc cutters makes a start on the rock at a point lying on the far side of the central line which corresponds to the axis of rotation of the head, with respect to the pivot point of the associated supporting arm, and then moves along the path of pivoting of the arm beyond this central line and continues out to the perimeter of the opening. This means that each disc cutter is subject to very different conditions during the course of the pivoting movement of its supporting arm. In particular, each disc cutter starts a small distance from the central line, this distance decreasing until the central line has been crossed. Following this, the disc cutter is still operating in the vicinity of the central cutting area. As will be explained later, this is inefficient. Moreover, the machine is restricted to the use of only two disc cutters.